Substituted indoles are useful as pharmaceutical agents. Examples of substituted indoles used as pharmaceutical agents and the preparation thereof include the anti-inflammatory agents indomethacin and tropesin, the antihistamine mebhydroline, and the vasodilator vinpocetine. Other examples of indole compounds used as pharmaceutical agents are indole compounds such as disclosed in U.S. patent application Ser. No. 10/198,384 (US2004/0024190) the contents of which are incorporated herein by reference and useful as HCV polymerase inhibitors in the treatment of HCV infections.
A convenient method for preparing aryl-substituted indoles is by a palladium catalyzed cross coupling reaction, such as for example Negishi cross coupling (E. Negishi, S. Baba, J. Chem. Soc. Chem. Communications, 1976, 596-597; S. Baba, E. Negishi, J. Am. Chem. Soc., 1976, 98, 6729-6731), or Suzuki cross coupling (J. Hassan et al., Chem Rev., 2002, 102, 1359 and N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457). The methodology of Negishi coupling was developed for Csp2-Csp2 or Csp2-Csp bond formation between alkenyl or aryl halides and organometallic reagents including organoaluminum and organozinc reagents (Csp2 or Csp) via palladium-catalyzed cross coupling (Scheme I).

Cross coupling reactions have been known to have substrate requirements, possibly as a result of the steric and electronic demand of catalysts. Because of the substrate requirements there are no uniform optimal conditions suitable for a broad range of substrates. Therefore, extensive screening of variables and their combinations is often necessary to develop a practical and economical manufacturing process using this methodology. Important variables often include, but are not limited to selection of metal catalysts, such as Pd, Ni, Pt etc, ligands, such as mono-dentate triphenylphosphine (Ph3P), tri-p-tolylphosphine (p-Tol3P), tricyclohexylphosphine (PCy3), tri-t-butylphosphine (t-Bu3P), (Cy2P(Ph-Ph)) and bi-dentate 1,1′-bis(diphenylphosphino)ferrocene (dppf), 1,4-bis(diphenylphosphino)ferrocene (dppb) etc., solvents, such as tetrahydrofuran (THF), dimethoxyethane (DME), dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP) etc., and temperature and bases in the case of the Suzuki reaction such as K2CO3.